#3 A champion is entitled to a mandatory rematch if he/she loses it
According to this rule, if a champion loses his/her title, they have the opportunity to invoke the rematch clause. As a result, they get the opportunity to regain their lost title. AJ Styles recently used his rematch clause in order to get back the US Title from Baron Corbin. Although he was not successful, AJ and Corbin delivered a good match.
But there have been times when a champion didn't get their mandatory rematch for the title they lost. "The Eater of Worlds" Bray Wyatt is one of the Superstars who moved on to other feuds without getting a rematch for his WWE title.
WWE even had a feud between AJ and Shane at Wrestlemania 33 for this reason. Styles was not happy with Shane as he did not his rematch for the WWE title which he lost and as a result took out his frustration on the SD Live Commissioner.